1. Field of the Invention
The invention relates to materials for thermal barrier coatings, and more particularly to partially-alloyed zirconia powders for use with plasma spray deposition processes.
2. Description of Related Art
Ceramic thermal barrier coatings (TBCs) have been successfully used in industrial gas turbines, aircraft engines, marine propulsion, and other hot metal applications for several years. One material is that has been used for such coating applications is zirconia (ZrO2) stabilized by about seven weight percent yttria (Y2O3), a material also referred to as 7YSZ. Generally, coatings from this material provide a favorable combination of properties that include low thermal conductivity, high thermal expansion coefficient, and phase stability to a relatively high temperature range. In some cases, uses of TBCs with 7YSZ can result in a temperature reduction of up to 170° C. (300° F.) at the underlying metal surface, thus improving durability of the metal component and allowing increased engine performance. Demands for greater engine efficiency, higher performance, and increased durability have created a need for improved coatings with even better protective properties.
Deposition of the TBC may be accomplished using, for example, a plasma spray process. In this process, ceramic powder feedstock is injected into a high velocity plasma stream where it is simultaneously melted and propelled toward a substrate. When the melted particles impact the substrate they solidify to form “splats,” which accumulate to form the TBC. The amount of the powder feedstock that actually becomes part of the resulting coating is a measure of deposition efficiency. Deposition efficiency may be generally defined as the ratio of the coating weight to the weight of total feedstock. Improving deposition efficiency remains an ongoing goal in the coating industry in order to both improve deposition rates and reduce material loss.